import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        String[] nums = s.split(" ");
        int num1 = Integer.parseInt(nums[0]);
        int num2 = Integer.parseInt(nums[1]);
        int count = 0;
        int[][] dp = new int[num1][num2];

        for(int i = 0; i < num1; i++){
            for(int j = 0; j < num2; j++){
                dp[i][j] = 1;
            }
        }
        for(int i = 0; i < num1; i++){
            for(int j = 0; j < num2; j++){
                if(dp[i][j] == 1){
                    count += 1;
                    if(i+2<num1){
                        dp[i+2][j] = 0;
                    }
                    if( j+2<num2){
                        dp[i][j+2] = 0;
                    }
                }
            }
        }
        System.out.println(count);
        long a = 012;
        double x = 0x1234;
        System.out.println(true == true);
    }
}